At least three people were shot dead Thursday in clashes over Kenya's election re-run, prompting officials to delay the vote in four counties as the country's worst political crisis in a decade deepened.

The bloodshed stained Kenya's second presidential election in three months, worsening a fractious ballot that has been boycotted by opposition leader Raila Odinga and polarised east Africa's flagship democracy.

Two of the deaths occurred as protests raged in opposition strongholds in the west of the country, while the third person died in a Nairobi slum where clashes erupted between demonstrators and police.

The casualties raised to 43 the tally of people killed in election-related violence since the August election victory of President Uhuru Kenyatta, which was later overturned by the Supreme Court, prompting Thursday's re-run.

As voting drew to a close, election chief Wafula Chebukati made a televised address, saying the ballot would be postponed until Saturday in four protest-hit counties in the country's west: Kisumu, Homa Bay, Migori and Siaya.

The move, he said, was due to "security-related" challenges.

As Odinga's supporters hit the streets, others went to the polls to cast their ballots.

But, in stark contrast to the August election, several polling stations in key areas stood empty or welcomed only a handful of voters in an election likely to face more legal battles after its conclusion.

As voting headed to a close, police and hospital sources confirmed three people had been shot dead and at least 24 wounded, 11 of them by live rounds.

At Jaramogi hospital in Odinga's western stronghold of Kisumu, an AFP correspondent saw several people arriving covered in blood.

"This is crazy, they are shooting at us -- we are demonstrating and they shoot us!" said Samuel Okot, 20, who was sitting with his friend Joseph Ouma who had been shot in the knee and was howling in pain.

"What kind of country is this?

Threat of more bloodshed
The violence drew a sharp response from rights watchdog Amnesty International.

"With tensions running high there is a very real threat of further bloodshed as the election re-run takes place," said Justus Nyangaya, director at Amnesty International Kenya.

"We are calling on the police to only use force as a last resort -- unlawful police killings and other human rights violations must not be allowed to recur."

In Kisumu, 19-year-old George Odhiambo died from blood loss after being shot in the thigh in clashes which erupted after protesters barricaded roads and polling stations to block the vote, police and hospital sources said.

Police said another man was shot dead in Homa Bay, also in the west, "where a large mob attacked a small police facility" prompting officers to open fire "to protect themselves," a statement said.

A third man died after being shot in the head in Nairobi's Mathare slum, another hotspot in the capital where protesters tried to block the vote and where police fired water cannon and teargas to disperse demonstrators.

In the eastern port city of Mombasa, police said a man was stabbed as he was going out to vote, while in Kisumu a police officer was also wounded with a knife.

Also in Mombasa, police said protesters in the city's Bangladesh slum had smeared faeces on the walls of a primary school that was to be used as a polling station.

The election is the chaotic climax of a political drama that began when the Supreme Court overturned the victory of President Uhuru Kenyatta in the August 8 elections.

Pyrrhic victory for Kenyatta?
Kenyatta, who turned 56 on Thursday, is almost assured victory after veteran opposition leader Odinga withdrew, citing fears the poll would be marred by the same flaws which saw the August vote overturned.

"Today, no fair election can take place. The government wants to force us to vote, but we did not want to do it and we will not do it," said Austin Olang, a 26-year-old maths teacher in Kisumu.

Analysts say the boycott in east Africa's richest economy and one of its strongest democracies is likely to tarnish the credibility of Kenyatta's victory and deepen its worst political crisis since a 2007 election sparked politically-driven ethnic violence that left 1,100 dead.

In the first election, turnout was nearly 80 percent among the 19 million registered voters. Kenyatta secured victory with 54 percent of the vote, while Odinga came second with 45 percent.

Odinga, 72, is a veteran opposition leader who followed in the footsteps of his father and inherited a dynastic rivalry with Kenyatta whose father was the country's first post-independence president.

In areas loyal to Kenyatta, turnout was steady but still appeared to be far lower than during the first round.

But in Odinga's main strongholds, polling officials were left twiddling their thumbs.

Interfering, undermining
The decision to cancel the August poll was initially hailed as a service to democracy in a country plagued by disputed elections.

But the re-run has been dogged by chaos and acrimony, prompting western diplomats to blast Odinga and Kenyatta for fuelling division.